The present invention relates to the control of internal combustion engines. More specifically, the present invention relates to a method and apparatus to control a variable displacement internal combustion engine.
Regulatory conditions in the automotive market have led to an increasing demand to improve fuel economy and reduce emissions in current vehicles. These regulatory conditions must be balanced with the demands of a consumer for high performance and quick response from a vehicle. Variable displacement internal combustion engines (ICEs) provide for improved fuel economy and torque on demand by operating on the principal of cylinder deactivation. During operating conditions that require high output torque, every cylinder of a variable displacement ICE is supplied with fuel and air (also spark, in the case of a gasoline ICE) to provide torque for the ICE. During operating conditions at low speed, low load and/or other inefficient conditions for a fully-displaced ICE, cylinders may be deactivated to improve fuel economy for the variable displacement ICE and vehicle. For example, in the operation of a vehicle equipped with an eight-cylinder variable displacement ICE, fuel economy will be improved if the ICE is operated with only four cylinders during low torque operating conditions by reducing throttling losses. Throttling losses, also known as pumping losses, are the extra work that an ICE must perform when the air filling the cylinder must be restricted during partial loads. The ICE must therefore pump air from the relatively low pressure of an intake manifold through the cylinders and out to the atmosphere. The cylinders that are deactivated will not allow air flow through their intake and exhaust valves, reducing pumping losses by allowing the active cylinders to operate at a higher intake manifold pressure. Since the deactivated cylinders do not allow air to flow, additional losses are avoided because the trapped charge in the deactivated cylinders act as xe2x80x9cair springsxe2x80x9d during the compression and decompression of the air in each deactivated cylinder.
In past variable displacement ICEs, the switching or cycling between the partial displacement mode and the fun displacement mode was problematic. Frequent cycling between the two operating modes negates fuel economy benefits and affects the driveability of a vehicle having a variable displacement ICE. The operator""s driving habits will affect the number of times a variable displacement ICE will cycle between the partial and the full displacement mode, and the fuel economy benefits of a variable displacement ICE. Frequent cycling will also impact component life in a variable displacement ICE.
The present invention is a method and apparatus for the control of cylinder deactivation in a variable displacement engine. In the preferred embodiment of the present invention, an eight-cylinder internal combustion engine (ICE) may be operated as a four-cylinder engine by deactivating four cylinders. The cylinder deactivation occurs as a function of the load or torque required by the vehicle and driver behavior. According to the present invention, different driver behaviors will create different criteria for an operating mode switch from partial displacement to full displacement of a variable displacement ICE. The present invention characterizes drivers and their perceived requirements for driveability.
Referring to FIG. 1, a graph of fuel economy gain is shown with three types of drivers characterized. In alternate embodiments of the present invention, any number of driver types may be characterized. A soft pedal or conservative driver is a driver that would be the most likely to monitor fuel economy for a variable displacement ICE. This type of driver is very likely to be dissatisfied if the claimed fuel economy benefits are not met. Operation in a partial displacement mode should be maximized for this type of driver.
A normal driver would utilize a normalized or nominal cycling schedule between partial and full displacement in a variable displacement ICE.
An aggressive driver is not likely to be in a partial displacement mode for any extended period of time due to high power demand and brake and accelerator pedal dynamics. The aggressive driver will realize less fuel economy gain than a conservative or normal driver and will be dissatisfied if the cylinder deactivation detracts from the desired driving experience. The aggressive driver would force numerous switching cycles if the control of the displacement of the variable displacement ICE used a nominal calibration.
Fuel economy for a variable displacement ICE should be maximized for soft pedal drivers and normal drivers, as their driving behaviors will allow superior fuel economy without any perceived decrease in performance. Aggressive drivers will not be as concerned with the fuel economy benefits of a variable displacement engine, as they favor performance. The present invention maximizes the amount of time spent in partial displacement mode for a soft pedal driver and a normal driver while maintaining the same performance and driveability of a fully-displaced ICE for an aggressive driver.
The engine control system of the present invention can characterize the type of driver using numerous sensor inputs such as an accelerator pedal position sensor, a brake pedal sensor, a manifold air pressure sensor, a throttle position sensor, and other traditional sensors used in the control of an ICE. By monitoring these sensor inputs over time, the engine control system will characterize the driver and then utilize calibrated switch points for each type of driver that will allow a soft-pedal driver or a normal driver to quickly enter the partial displacement mode, while preventing unacceptable frequent cycling between displacement modes for an aggressive driver. In alternate embodiments of the present invention, adaptive switching points may be used that continually change in response to driver behavior. A variable filter for sensor inputs having calibrated hysteresis pairs may also be used in the present invention to reduce cycling busyness.